Methods and apparatus for producing thin sheets of material, such as metal, plastic, rubber, and the like, are generally similar regardless of the material. In the steel industry, for example, these methods and apparatus as applied to the formation of steel sheets give rise to problems common to the production of sheets of all such materials.
The steel industry today, particularly in the United States, is facing increased labor costs and increasing aggressive foreign competition, while still using, in large part, outdated manufacturing technologies. As a consequence, the larger integrated steel producers, with their inefficient and labor intensive manufacturing processes, are losing their customary share of the market and, consequently, are being forced to reduce or cease production in many of their product lines. The larger American steel makers today produce less than half of this country's steel shipments, while the smaller, more specialized companies have been able to remain competitive and even increase market share. As a result, the trend in the steel manufacturing industry is away from the large integrated plants to the smaller, more specialized "mini-mills", which have the flexibility to incorporate advances in technology into their manufacturing processes, which allows them to operate with lower labor costs and, hence, more efficiently. However, many of these mini-mills are relocating or starting up outside of this country where labor costs are lower. A reversal of this trend and a restoration of economic viability to the steel industry in this country can at least partially be achieved through the development and use of new manufacturing technologies for the production of steel sheets, for example, that are aimed at increased productivity, lowered production costs, and improved product quality.
Many of the new manufacturing processes being developed for the production of steel sheets are directed at replacing the labor and capital intensive processes and techniques of the rolling mill in which steel sheets are produced. In a typical steel mill, once a slab of steel has been produced it must be mechanically worked, usually by a rolling process, in what are known as "rolling mills," in order to produce various finished products, such as plates or sheets of metal. Inasmuch as labor is the major cost associated with the operation of these rolling mills, a need exists for a method and apparatus for producing finished metal products, such as sheet steel, that reduce the high labor costs associated with these rolling mills and, in turn, makes steel producers more competitive.
In the past, and to a large extent at the present time, sheets of metal, such as steel or aluminum, have been produced by a process that utilizes ingot molds made of cast iron, for example, to produce oblong ingots, which are mechanically rolled into sheets. Another method for producing sheets of metal is a continuous casting method wherein molten metal, teemed in an elevated tundish, flows through an opening in the bottom thereof into a water-cooled cooper mold. Within this mold, the metal cools and solidifies as it is continuously advanced toward the rolling apparatus where it is mechanically rolled into sheets. However, both the ingot-mold method and the continuous casting method are both capital and labor intensive processes.
One technique that has reduced the expenses associated with the rolling mill is a direct casting process for sheets of metal. In direct casting, a layer or sheet of metal is drawn directly from a tundish of heated substantially molten metal. With this method, a sheet of metal thinner than that produced by the tundish and copper mold of the continuous casting method can be produced, thereby reducing the amount of subsequent mechanical work that is, rolling, necessary to produce extremely thin sheets of metal. However, direct casting does not eliminate the need for subsequent mechanical working because the use of soft, heated metal limits the thinness of the sheet metal that can be drawn from the tundish. Hence, a relatively significant amount of additional mechanical working is necessary to achieve the extremely thin sheets of metal with desirable mechanical properties that many industries desire.
Thus, a need exists for a method and apparatus for producing extremely thin sheets of material having high strength characteristics which substantially replaces the present method and apparatus of the rolling mill.